Color center in amethyst quartz   总被引：1，自引：0，他引：1  

Lehmann G  Moore WJ 《Science (New York, N.Y.)》1966,152(3725):1061-1062

Treatment with x-rays increased the intensity of color of natural amethyst up to fivefold, and an electron paramagnetic resonance spectrum was detected. The intensity of the spectrum was proportional to the intensity of the optical absorption near 545 mmicro. The EPR spectrum of the color center corresponded to a positive hole trapped on a substitutional Fe(3+) ion in the quartz structure. We ascribe the color to a charge-transfer transition, Fe(4+) + O(2)- --> Fe(3+) + O(1-).  相似文献   

Structure of yeast poly(A) polymerase alone and in complex with 3'-dATP     

Bard J  Zhelkovsky AM  Helmling S  Earnest TN  Moore CL  Bohm A 《Science (New York, N.Y.)》2000,289(5483):1346-1349

Polyadenylate [poly(A)] polymerase (PAP) catalyzes the addition of a polyadenosine tail to almost all eukaryotic messenger RNAs (mRNAs). The crystal structure of the PAP from Saccharomyces cerevisiae (Pap1) has been solved to 2.6 angstroms, both alone and in complex with 3'-deoxyadenosine triphosphate (3'-dATP). Like other nucleic acid polymerases, Pap1 is composed of three domains that encircle the active site. The arrangement of these domains, however, is quite different from that seen in polymerases that use a template to select and position their incoming nucleotides. The first two domains are functionally analogous to polymerase palm and fingers domains. The third domain is attached to the fingers domain and is known to interact with the single-stranded RNA primer. In the nucleotide complex, two molecules of 3'-dATP are bound to Pap1. One occupies the position of the incoming base, prior to its addition to the mRNA chain. The other is believed to occupy the position of the 3' end of the mRNA primer.  相似文献   

Energetics, patterns of interaction strengths, and stability in real ecosystems     

de Ruiter PC  Neutel AM  Moore JC 《Science (New York, N.Y.)》1995,269(5228):1257-1260

Ecologists have long been studying stability in ecosystems by looking at the structuring and the strengths of trophic interactions in community food webs. In a series of real food webs from native and agricultural soils, the strengths of the interactions were found to be patterned in a way that is important to ecosystem stability. The patterning consisted of the simultaneous occurrence of strong "top down" effects at lower trophic levels and strong "bottom up" effects at higher trophic levels. As the patterning resulted directly from the energetic organization of the food webs, the results show that energetics and community structure govern ecosystem stability by imposing stabilizing patterns of interaction strengths.  相似文献   

Thoroughly modern reptiles     

Moore RT 《Science (New York, N.Y.)》1993,259(5103):1810-1811

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AN ADDITIONAL NOTE ON "THE OOLITIC AND PISOLITIC BARITE FROM THE SARATOGA OIL FIELD,TEXAS"     

Moore ES 《Science (New York, N.Y.)》1917,46(1188):342

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Total carbon and nitrogen abundances in lunar samples     

Moore CB  Lewis CF  Gibson EK  Nichiporuk W 《Science (New York, N.Y.)》1970,167(3918):495-497

Total carbon and nitrogen abundances were determined by using combustion-gas chromatographic techlniques. Weighited mean analyses for butlk fines were 225 and 140 ppm total carbon and 150 anid 100 ppm total nitrogen. Total carbon in fine breccia was 230 ppm; in coarse breccia, 100 ppmn; in fine-grained rock, 70 ppm; and in mediumn-grained rock, 64 ppm. The finest sieved fraction had the highest carbon content. Total nitrogen in fine breccia was 125 ppm; in coarse breccia, 100 ppm; in fine-grained rock, 115 ppm; and in medium-grained rock, 30 ppm. The total carbon and nitrogen finies appeat to be mixtuires of indigenous lunar material togetheer with meteoritic and solar wind components.  相似文献   

Smoking, Arteriosclerosis, and Age     

Moore GE 《Science (New York, N.Y.)》1963,139(3559):1096

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The "soil" of Mars (viking 1)     

Shorthill RW  Moore HJ  Scott RF  Hutton RE  Liebes S  Spitzer CR 《Science (New York, N.Y.)》1976,194(4260):91-97

The location of the Viking 1 lander is most ideal for the study of soil properties because it has one footpad in soft material and one on hard material. As each soil sample was acquired, information on soil properties was obtained. Although analysis is still under way, early results on bulk density, particle size, angle of internal friction, cohesion, adhesion, and penetration resistance of the soil of Mars are presented.  相似文献   

Odor-mediated push-pull pollination in cycads     

Terry I  Walter GH  Moore C  Roemer R  Hull C 《Science (New York, N.Y.)》2007,318(5847):70

The reproductive organs of some plants self-heat, release scent, and attract pollinators. The relations among these processes are not well understood, especially in the more ancient, nonflowering gymnosperm lineages. We describe the influence of plant volatiles in an obligate pollination mutualism between an Australian Macrozamia cycad (a gymnosperm with male and female individuals) and its specialist thrips pollinator, Cycadothrips chadwicki. Pollen-laden thrips leave male cycad cones en masse during the daily thermogenic phase, when cone temperatures and volatile emissions increase dramatically and thrips are repelled. As thermogenesis declines, total volatile emissions diminish and cones attract thrips, resulting in pollination of female cones. Behavioral and electrophysiological tests on thrips reveal that variations in b-myrcene and ocimene emissions by male and female cones are sufficient to explain the observed sequential thrips' repellence (push) and attraction (pull). These dynamic interactions represent complex adaptations that enhance the likelihood of pollination and may reflect an intermediate state in the evolution of biotic pollination.  相似文献   

Lunar transient phenomena: topographical distribution     

Middlehurst BM  Moore PA 《Science (New York, N.Y.)》1967,155(3761):449-451

The sites named in nearly 400 reports of lunar transient phenomena fall into three classes: (i) sites peripheral to the maria, (ii) ray craters, and (iii) ring plains with dark or partially dark floors; none are known in the rugged highland area of the southeast (International Astronomical Union, 1964; classically southwest) quadrant. Permanent records are few; the sites where known are consistent with the visual records.  相似文献